The SQUID is one of the most sensitive magnetic field devices in the prior art, and it can be used for wide range of applications, including biology, medicine, geology, systems for semiconductor circuit diagnostics, security MRI and even cosmology research. In recent years, arrays of coupled oscillators have been considered as a general mechanism for improving signal detection and amplification. Theoretical and experimental studies can be interpreted to show that arrays of SQUIDs can yield comparable improvements in signal output relative to background noise, over those of a single SQUID device.
A peculiar configuration that has gained considerable attention among the physics and engineering community is that of multi-loop arrays of JJs with non-uniformly distributed loop areas. Typically, each loop contains two JJs, i.e., a standard DC-SQUID, but their size vary from loop to loop. These types of unconventional geometric structures of JJs are known to exhibit a magnetic flux dependent voltage response V(φe), where φe denotes an external magnetic flux normalized by the quantum flux, that has a pronounced single peak with a large voltage swing at zero magnetic field. The potential high dynamic range and linearity of the “anti-peak” voltage response render the array an ideal detector of absolute strength of external magnetic fields. These arrays are also commonly known as Superconducting Quantum Interference Filters (SQIFs).
Improving the linearity of SQIFs is critical for developing advanced technologies, including: low noise amplifier (LNA) that can increase link margins and affect an entire communication system. SQIFs can also be used in unmanned aerial vehicles (UAVs), where size, weight and power are limited, and “electrically small” antennas that can provide acceptable gain are needed. SQIFs can also be used in land mine detection applications. But for these applications, it is desired to improve the linear response of the SQIF device.
A standard approach to improve linearity and dynamic range of a SQIF device can be to employ electronic feedback, but this approach can unfortunately limits the frequency response of the system. So, for applications that require a large signal frequency response, feedback can not be used. Series arrays of identical DC-SQUIDs have also been studied as an alternative approach to produce an anti-peak voltage response, but the linearity appears to be inferior to that of non-uniform loops.
In view of the above, it is an object of the present invention to provide a SQIF that can incorporate individual array cells of bi-SQUIDS, which can contain three JJs, as opposed to the standard practice of two JJs per loop. Another object of the present invention if to provide a SQIF amplifier with improved linear repsonse when compared to SQIF that are comprised of arrays of conventional DC-SQUIDs (SQUIDs with two JJs). Still another object of the present invention is to provide a novel linearization method for maximizing the voltage response and dynamic range of a SQIF by manipulating the critical current, inductive coupling between loops, number of loops, bias current, and distribution of loop areas of the array cell bi-SQUIDs. Yet another object of the present invention is to provide a SQIF array where bi-SQUIDs can be integrated into a two-dimensional structure in both serial and parallel configurations to deliver superior linearity at appropriate impedance. Another object of the present invention is to provide a SQIF and methods for manufacture that can be easily tailored in a cost-effective manner to result in a SQIF having bi-SQUID array cells that has been optimized according to the user's needs.